Electric circuit breaker



Oct. 7, 1941. w. F. SKEATS ELECTRIC CIRCUIT BREAKER Filed Sept. 13, 1939Inventor. WiIFred F. SKeats, y WW (9W Hi Attorney.

armed Oct. 7, 1941 2,258,226 ELECTRIC CIRCUIT BREAKER Wilfred F. Skeats,Lansdowne, Pa., assignor to General Electric Company, a corporation ofNew York Application September 13, 1939, Serial No. 294,644

6 Claims.

My invention relates to electric circuit breakers, particularly tocircuit breakers of the fluid jet or blast type wherein an arcextinguishing fluid, such as oil, is directed under pressure through thearc gap formed upon opening of the circuit. More specifically, myinvention relates to the oil blast type circuit breaker wherein arcpressure is utilized to force 011 or the like through the interruptinggap to extinguish arcing, and has for its principal object .theprovision of means for appreciably increasing the interrupting capacityof this type breaker, particularly in the case of heavy overload andshort circuit currents.

Where are pressure generated at an auxiliary or initially formed are isutilized to drive oil through another or interrupting are, there willalso be formation of gas at the pressure generating are which may incertain cases mix with the interrupting oil blast. This gas is highlyheated and therefore has poor dielectric characteristics so that itspresence in the vicinity of the interrupting gap is undesirable forobvious reasons.

In accordance with the present invention, the arc pressure, while beingutilized in the usual manner to effect interruption by means of a liquidblast, directs the gas formed at the pressure are away from theinterrupting blast. The gas is then for practical purposes trapped untilthe interrupting operation has been completed.

My invention will be more fully set forth in the following descriptionreferring to the accompanying drawing, and the features of novelty whichcharacterize my invention will be pointed out with particularity in theclaims annexed to and forming a part of this specification.

Referring to the drawing, the single figure thereof is an elevationalview partly in section of an oil circuit breaker in the open circuitposition embodying the present invention.

The oil circuit breaker illustrated by way of example is of the combinedoil blast and impulse type and comprises a main casing I that is dividedinto a switch chamber 2 for housing the relatively movable contacts andare extinguishing structure, and a piston cylinder 3 arranged to be incommunication with the switch chamber through a passage 4. The casing Iwhich is provided with insulating supports at I' is composed of metalsuch as bronze for example and constitutes one terminal of the circuitbreaker, the other terminal of which is suitably connected to themovable contact rod 5. This contact is slid- I ably guided for coactionwith the relatively fixed contact structure in an insulating bushing 8that is in turn suitably mounted, as indicated at I and 1', in the coverplate 8 of the switch casing.

The complete contact structure comprises a fixed butt contact 8 having athreaded extension III that is secured to a frustro-conical portion IIformed on the lower wall of the switch casing. The fixed contact istherefore in direct electrical contact with one switch terminal, i. e.,the metal casing I.

Interposed between the movable rod contact 5 and the fixed contact is anintermediate or floating contact I2 that is carried by an insulatinsupport I3 that is in turn resiliently mounted on the lower wall, asindicated at I4, of the insulating baiiie I5. The contact I2 is slidablyguided in the battle as illustrated, and for practical purposes seals atall times the baffle aperture I2. In the open circuit position shown,the floating contact I2 is biased at I 4 upwardly and away from thefixed contact 8 so that a short gap (approximately separates thecontacts.

When the circuit breaker is to be closed, the rod contact 5 is loweredby suitable operating means (not shown), first to engage the upper buttcontact surface of floating contact I2, and subsequently upon continuedmovement to complete the circuit by pressing the floating contactagainst the fixed contact 9. The reverse order is followed upon openingof the circuit, the arc initially formed between the contacts 8 and I2being utilized to generate pressure for assisting in interrupting theare between the contacts I2 and 5 in a manner that is now well-known inthe art.

The breaker casing is filled with a suitable arc extinguishing liquid,such as oil, to the level indicated so that the baflie Ii within whichare interruption takes place is practically immersed. This baflie formstwo chambers within the main chamber 2, the chamber below the battlebeing in effect a pressure chamber, and the one above the baiile beingan exhaust chamber. The baffle is provided with a cross blast passage I6that communicates at its lower end with the pressure chamber, and afterpassing transversely through the arc path between the contacts I and I2,exhausts at I6 to the upper chamber. The baflle I5 is constructed of amechanically strong insulating material and is positioned in the casingbetween the casing shoulder I I and an insulating sleeve I8 that is inturn firmly engaged by a positioning ring I! having adjusting means 20secured to the casing cover 8. The lower end of the tubular insulatingbushing 6 enclosing the movable contact seats on the upper wall of thebattle I5 which is provided with an aligned aperture ii for the movablecontact.

The structure so far described is known as the oil-blast type circuitbreaker wherein two arcs are formed in series, one of said arcs beingacted upon by pressure generated at the other arc. At low currents,however, additional pressure is often required and to this end theimpulse feature involving a piston is added.

The cylinder 3 is provided with a piston 33 having an operating rod 23actuated by means suitably related to the operating means for themovable contact. Such operating means form no part of the presentinvention and may for example be of the type disclosed and claimed in U.S. Patent 2,025,549, granted December 24, 1935 to D. 0. Prince for"Operating mechanism for electric circuit breakers." The arrangement issuch that the piston is depressed as the contact is raised to open thecircuit.

The piston is also provided with a resetting spring 24 seated between astationary spider 26 and a shoulder 23' on the piston rod. A disktypeone-way valve 23 coacts with the piston as illustrated for the purposeof permitting oil to flow back into the iowenpart of the casing upon thereturn or resetting stroke of the piston. Accordingly, when the piston22 is driven downward from the position shown, oil is forced from thecylinder 3 through the passage 4 upwardly into the pressure chamberbeneath the baifle l5, from whence it can escape only by way of thetransverse blast passage it into the upper exhaust chamber.

In the case of low or moderate load currents, the oil driven solely bythe piston across the are between contacts I and i2 would generally beeffective to interrupt arcing within a cycle or so. However, in the caseof large overload or short circuit currents, the pressure generated atthe initially formed are between contacts 9 and I2 within the pressurechamber may be so great that the motion of the piston is actuallyreversed. In such a case, the piston is obviously ineffective andfailure of the breaker may resuit.

For the purpose of utilizing the are pressure at the initially formedare to the best advantage in such a case, a valve plate 21 is mounted onthe frustro-conical portion ll so that it may form a partition betweenthe arc pressure chamber and the cylinder 3. A plurality of disk-typeoneway valves 28 are mounted on the valve plate to control the openings28' communicating with the cylinder passage 4 and the arc pressurechamber.

As shown, the valves which are slidably guided on the post supports 29open freely when the pressure in the piston cylinder exceeds that in thearc pressure chamber, but seat tightly to close the openings 23' whenthe arc chamber pressure exceeds that in the piston cylinder.

Therefore, in the case of the heavy current interruptions previouslyreferred to, the arc pressure, when it exceeds the piston pressure,causes closing of the valves 28 and drives oil from the pressure chamberthrough the transverse blast passage ii to interrupt the high currentarc. The are pressure is therefore utilized for are interruption insteadof being partially dissipated in causing reversal of the piston. It willbe apparent that in other cases where the piston is eifective, thepressure generated by the initial arc serves to augment or supplementthe piston pressure to aid in interrupting the arc. That is,

caused looping of the arc.

the oil blast velocity is somewhat increased. The exhaust chamber issuitably vented at 3' to the usual separating chamber (not shown).

In the case of large currents, the pressure generating arc formedbetween contacts 3 and i2 may be bowed or looped laterally by themagnetic forces so as to be of excessive length. This is due to thewell-known magnetic effect in a looped conductor carrying current, andmay cause excessive pressure in the arc chamber. For controlling thepressure generating are so that it does not appreciably exceed in lengththat of the gap between contacts I and it, a conducting ring 33, isemployed to prevent or limit outward bowing or looping of the are beyonda certain point. The ring 33 is mounted on an insulating cylindricalspacer 3| so as to surround in spaced relation thearc gap and iscomposed of a metal, such as copper, and is held in position by thevalve guide posts 33.

In case the arc is looped by magnetic forces into contact with the ring33. it will be noted that the magnetic forces established by the arccurrent flowing at right angles from the contact I: through the ring tothe valve plate act in a direction opposing the forces that originallyThe are control and valve arrangements above described form no part ofthe present invention and are fully described and claimed in a copendingapplication, Serial No. 294,642, filed concurrently herewith by D. C.Prince for Electric circuit breaker," and assigned to the same assigneeas the present invention.

When large currents are to be interrupted the gas formation due to theare heat is greater. Therefore, highly heated arc gases may be carriedby the oil blast into the transverse passage I so as to cause diflicultyin clearing the circuit. That is, let it be assumed that a bubble ofhighly heated are formed gas is passing through the passage I at thetime of or slightly after a current interruption. Since this gas hascomparatively low dielectric strength, the interrupting gap is poorlyinsulated with respect to the recovery voltage and restriking of the arcmay occur either immediately or after a short interval.

This is prevented in the present case in accordance with my invention bya form of bame arrangement between the pressure generating arc and theintake of the blast passage which not only directs the gas away from theintake but tends to segregate or isolate the gas for a short time untilinterruption is complete. Specifically, the bailie arrangement comprisesa spout or the like 32 extending beneath the bafile 15 at the intakeofthe blast passage ll into the pressure chamber and ridge or lip 33mounted on thearc control ring 33 for example at a position between thearc gap and the spout 32. The'spout 33 is offset as far as possiblewithrespect to the pressure generating arc and the lip 33 is preferablyof crescent or semi-circular shape as illustrated so as partly tosurround the pressure generating break and to shield the spout intakefrom the arc gases. The gases are therefore prevented from being blowndirectly into the spout and are temporarily pocketed and isolatedbeneath the bailfe at 32'. Therefore the arc gases at the break 9- areisolated with respect to the arc extinguishing liquid blast through thepassage I. A small bleed vent at ii in the baflie permits the pressurechamber to reflil with oil after an interrupting operation and allowsthe gases trapped at 32' to escape to the top of the battle after aninterrupting operation.

In certain cases, the inertia of the oil blast is such that the oilcontinues to move even after the piston 22 is stopped. This tends tocause a void in the region of the interrupting break in the passage ISwith the result that re-ignition of the arc may occur due to the lowdielectric strength at the interrupting break. I have found that thiscan be prevented by venting the blast passage at an intermediate pointupon predetermined separation of the contacts. Specifically, this isdone by providing an aperture, or apertures, indicated at 6' in thebushing 6 above the oil level so that oil from the bushing isimmediately forced into the passage IS in such cases. That is, theoutgoing oil blast draws oil into the interrupting gap from the bushing6 instead of creating a momentary partial vacuum in the gap which wouldbe the case were the vent 6' not provided. I have found that thisresults in improved interrupting performance.

It should be understood that my invention is not limited to specificdetails of construction and arrangement thereof herein illustrated, andthat changes and modifications may occur to one skilled in the artwithout departing from the spirit of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. An electric circuit breaker oi' the fluid blast type comprisingrelatively movable contact structure arranged to form two breaks inseries, an arc extinguishing liquid in which said breaks are formed,bafile structure for directing a liquid blast under influence of the arcpressure generated at one of said breaks through the other break toextinguish arcing, means adjacent to said pressure generating are forinitially deflecting said liquid blast and the gas formed thereat, andadditional means associated with said batlie for pocketing gas sodeflected so that it is isolated with respect to said arc interruptingliquid blast.

2. An electric circuit breaker or the fluid blast type comprisingrelatively movable contact structure arranged to form two breaks inseries, an arc extinguishing liquid in which said breaks are formed,baffle structure for directing a liquid blast under influence of the arcpressure generated at one of said breaks through the other break toextinguish arcing thereat, said baflie having a transverse passagecommunicating with the region in which said pressure generating arc isformed, means for deflecting gas generated at said pressure break awayfrom said passage, and means forming an extension of said blast passageextending beneath said bafile into said region in offset relation tosaid deflecting means for isolating gas formed at said pressuregenerating break with respect to the interrupting liquid blast in saidtransverse passage.

3. An electric circuit breaker of the fluid blast type comprisingrelatively movable contact structure arranged to form two breaks inseries, an arc extinguishing liquid in which said breaks are formed,bafiie structure for directing a liquid blast under influence of the arcpressure generated at one of said breaks through the other break toextinguish arcing thereat, a second deflecting bafile partly surroundingin generally concentric relation said pressure generating break fordeflecting gas formed at said break in a direction away from said areinterrupting liquid blast, and means for temporarily isolating said gasat a point near the entrance of said blast to said first-named baiiiestructure.

4. An electric circuit breaker of the fluid blast type comprisingrelatively movable contact structure arranged to form two breaks inseries, an arc extinguishing liquid in which said breaks are formed, abaille having a transverse blast passage for directing a liquid blastunder influence of the arc pressure generated at one of said breaksthrough the other break formed in said passage to extinguish arcing,means forming an extension of said blast passage extending in adirection transversely of said baiile and into the region of saidpressure generating break, said extension being appreciably offset withrespect to said break, and a baflie member extending in the oppositedirection disposed between said pressure generating break and saidextension and ofiset with respect to said extension passage fordeflecting gas formed at said pressure generating break away from theextension passage whereby said gas is isolated with respect to the arcinterrupting liquid blast.

5. An electric circuit breaker of the liquid blast type comprisingseparable contacts, an arc extinguishing liquid in which said contactsseparate, insulating means in which said contacts operate forming anenclosure for the movable contact and a blast passage traversing the arcpath formed upon separation of said contacts, mechanical means fordriving liquid at high velocity through said passage to interrupt thearc therein so that due to its inertia said liquid tends to evacuatesaid passage, and. means defined by said insulating means communicatingwith said passage at an intermediate point only after predeterminedcontact separation within said insulating means for venting it toatmospheric pressure whereby the inertia of said liquid blast isineffective to create a partial vacuum in said passage and said passageis maintained substantially full of liquid after arc interruption.

6. An electric circuit breaker of the liquid blast type comprising fixedand movable contacts, an arc extinguishing liquid, insulating meansforming a blast passage traversing the arc path formed upon separationof said contacts and enclosing the movable contact, a piston for drivingliquid at high velocity through said passage to interrupt the arctherein, and an air vent in said insulating means disposed laterally ofsaid movable contact arranged to be opened in accordance withpredetermined contact opening movement to communicate with said passageat a point adjacent to said are whereby air pressure acting on said areextinguishing liquid precludes formation of a vacuum in said passageafter arc interruption when said piston suddenly stops.

WILF'RED F. SKEATS.

